1. Field of the Invention
The technique disclosed in the present specification relates to a transistor. In particular, the technique relates to a transistor that uses a 2DEG formed by a hetero-junction as a channel.
2. Description of the Related Art
FIG. 3 of Japanese Patent Laid-Open Application Publication No. 2007-273856 discloses a High Electron Mobility Transistor (hereinafter “HEMT”). The HEMT utilizes a two dimensional electron gas (hereinafter “2DEG”) as a channel. The 2DEG is generated by a hetero-junction of a GaN layer and an AlGaN layer. With this HEMT, a p-type GaN layer is formed in a position adjacent to the GaN layer that functions as the channel (as such, hereinafter referred to as “channel GaN layer”). When the gate voltage is turned off, the depletion layer expands from the p-type GaN layer to the channel GaN layer, and the 2DEG dissipates. Thus, when the gate voltage is in the off state, the HEMT is off. When the gate voltage is turned on, electrons are attracted to the hetero-junction, and 2DEG is formed. In this way, the HEMT is turned on. In this manner, this technology achieves a normally off type HEMT by forming a p-type GaN layer in a position adjacent to the channel GaN layer.